Thanks for your help.
In the end I figured out what was wrong, posting here as it might help others. It turned out this was indeed a syntax issue in the addHeader() method, which seems to add automatically the semi-column.
This is wrong:
https.addHeader("auth-token:", "uJU7AL0FbiGW9TgMt8lHOu8cLs31eFgZ");
This is correct:
https.addHeader("auth-token", "uJU7AL0FbiGW9TgMt8lHOu8cLs31eFgZ");